Most of conventional multiphase voltage regulators adopt individual modulators for each phase or constant switching frequency control. The individual modulators receive synchronous ramp signals, respectively, for realizing interleaved phase operation. The constant switching frequency control achieves interleaved operation with multiple phases by use of fixed phase sequence and time intervals. The fixed-phase-sequence interleaved operation uses synchronous constant-time phase-shifted signals to drive the parallel coupled phases.
As shown in FIG. 1, a conventional fixed-phase-sequence interleaved voltage regulator 10 includes multiple channels 12, 14, and 16 to convert an input voltage Vin into an output voltage V0, an error amplifier 36 to monitor the output voltage V0 to generate an error signal Vc, an adder 30 to combine the error signal Vc with the channel current IL1 of the channel 12 to generate an error signal Vc1, a modulator 18 having a comparator 20 to compare the error signal Vc1 with a ramp signal Vramp1 to generate a control signal PWM1 to drive the channel 12, an adder 32 to combine the error signal Vc with the channel current IL2 of the channel 14 to generate an error signal Vc2, a modulator 22 having a comparator 24 to compare the error signal Vc2 with a ramp signal Vramp2 to generate a control signal PWM2 to drive the channel 14, an adder 34 to combine the error signal Vc with the channel current ILN of the channel 16 to generate an error signal VcN, and a modulator 26 having a comparator 28 to compare the error signal VcN with a ramp signal VrampN to generate a control signal PWMN to drive the channel 16.
FIG. 2 is a circuit diagram of a conventional multiphase voltage regulator 40 with constant on-time control, which is also referred to as variable switching frequency control, and FIG. 3 is a waveform diagram of the multiphase voltage regulator 40. The multiphase voltage regulator 40 includes multiple channels 42, 44 and 46 to convert an input voltage Vin into an output voltage V0, an error amplifier 72 to monitor the output voltage V0 to generate an error signal Vc, an adder 66 to combine the channel current IL1 of the channel 42 with the error signal Vc to generate an error signal Vc1, a modulator 54 having a comparator 56 to compare the error signal Vc1 with a ramp signal Vramp1 to generate a signal Ramp1 as shown by the waveform 84, an on-time generator 48 to generate a constant on-time signal PWM1 as shown by the waveform 78 according to the signal Ramp1 to drive the channel 42, an adder 68 to combine the channel current IL2 of the channel 44 with the error signal Vc to generate an error signal Vc2, a modulator 58 having a comparator 60 to compare the error signal Vc2 with a ramp signal Vramp2 to generate a signal Ramp2 as shown by the waveform 82, an on-time generator 50 to generate a constant on-time signal PWM2 as shown by the waveform 76 according to the signal Ramp2 to drive the channel 44, an adder 70 to combine the channel current ILN of the channel 46 with the error signal Vc to generate an error signal VcN, a modulator 62 having a comparator 64 to compare the error signal VcN with a ramp signal VrampN to generate a signal RampN as shown by the waveform 80, and an on-time generator 52 to generate a constant on-time signal PWMN as shown by the waveform 74 according to the signal RampN to drive the channel 46.
The switching frequency of the multiphase voltage regulator 40 with constant on-time control varies with its loading, and thus the switching loss also varies with the loading. In other words, when the multiphase voltage regulator 40 operates with a lower switching frequency, its switching loss is small and thus it is superior to the multiphase voltage regulator 10 in term of efficiency. However, since the switching period of the multiphase voltage regulator 40 is not constant, it is unable to perform interleaved phase operation by dividing the switching period, as does the multiphase voltage regulator 10. That is, it is difficult for the multiphase voltage regulator 40 to achieve interleaved phase operation.
Therefore, it is desired a simple solution for implementation of constant on-time control for an interleaved multiphase voltage regulator.